XXX - Not complete.
Name
SGIX_resample
Name Strings
GL_SGIX_resample
Version
Last Modified Date: January 27, 2015
Revision: 2
Number
212
Dependencies
SGIX_subsample affects the definition of this extension
EXT_texture3D affects the definition of this extension
EXT_subtexture affects the definition of this extension
EXT_histogram affects the definition of this extension
EXT_convolution affects the definition of this extension
SGI_color_table affects the definition of this extension
Overview
This extension enhances the unpacking resampling capabilities
of the SGIX_subsample extension.
When pixel data is received from the client and an unpacking
upsampling mode other than PIXEL_SUBSAMPLE_RATE_4444_SGIX is
specified, the upsampling is performed via one of two methods:
RESAMPLE_REPLICATE_SGIX, RESAMPLE_ZERO_FILL_SGIX.
Replicate and zero fill are provided to
give the application greatest performance and control over the
filtering process.
However, when pixel data is read back to the client and a
packing downsampling mode other than PIXEL_SUBSAMPLE_RATE_4444_SGIX
is specified, downsampling is
performed via simple component decimation (point sampling). That is,
only the RESAMPLE_DECIMATE_SGIX is valid.
Issues
* this spec omits the packing downsampling mode. But I think
we will have to address it at some point, so I'm adding the
RESAMPLE_DECIMATE_SGIX as another tag to complement the unpacking
resample modes.
* In the public Khronos spec files and headers, these values
used to be used for some of the tokens:
#define GL_PACK_RESAMPLE_SGIX 0x842C
#define GL_UNPACK_RESAMPLE_SGIX 0x842D
#define GL_RESAMPLE_REPLICATE_SGIX 0x842E
#define GL_RESAMPLE_ZERO_FILL_SGIX 0x842F
#define GL_RESAMPLE_DECIMATE_SGIX 0x8430
These values corresponded to the internal SGI spec files and
(probably) to what was shipped on SGI IRIX systems supporting this
extension, but the spec was always inconsistent with these values.
Since SGI is long out of the graphics business, in order to reduce
incompatibility between tools pulling from the Khronos spec file
and tools pulling from the extension spec, the spec file has been
changed to match the extension.
New Procedures and Functions
None.
New Tokens
Accepted by the parameter of PixelStoref, PixelStorei,
GetBooleanv, GetIntegerv, GetFloatv and GetDoublev:
PACK_RESAMPLE_SGIX 0x842E
UNPACK_RESAMPLE_SGIX 0x842F
Accepted by the parameter of PixelStoref and
PixelStorei when the parameter is UNPACK_RESAMPLE_SGIX:
RESAMPLE_REPLICATE_SGIX 0x8433
RESAMPLE_ZERO_FILL_SGIX 0x8434
Accepted by the parameter of PixelStoref and
PixelStorei when the parameter is PACK_RESAMPLE_SGIX:
RESAMPLE_DECIMATE_SGIX 0x8430
Additions to Chapter 2 of the 1.1 Specification (OpenGL Operation)
None.
Additions to Chapter 3 of the 1.1 Specification (Rasterization)
3.6.1 Pixel Storage Modes
The following is added to Table 3.1:
Parameter Name Type Initial Value Valid Range
-------------- ---- ------------- -----------
UNPACK_RESAMPLE_SGIX integer RESAMPLE_REPLICATE_SGIX RESAMPLE_REPLICATE_SGIX
RESAMPLE_ZERO_FILL_SGIX
PACK_RESAMPLE_SGIX integer RESAMPLE_DECIMATE_SGIX RESAMPLE_DECIMATE_SGIX
3.6.3 Rasterization of Pixel Rectangles
Conversion to Uniform Sampling
------------------------------
This step is applied only if the PixelStore parameter
UNPACK_SUBSAMPLE_RATE_SGIX is set to something other than
PIXEL_SUBSAMPLE_RATE_4444_SGIX. If UNPACK_SUBSAMPLE_RATE_SGIX is set to
PIXEL_SUBSAMPLE_RATE_2424_SGIX or PIXEL_SUBSAMPLE_RATE_4242_SGIX then
the number of components per pixel is increased from two to three.
After upsampling, the data is treated as though it were RGB. When
this step is carried out the operation is controlled by the value
of the PixelStore parameter UNPACK_RESAMPLE_SGIX.
If UNPACK_RESAMPLE_SGIX is set to RESAMPLE_REPLICATE_SGIX then the first
component of the ith resulting pixel in a row is taken from the
first component of input pixel 2*floor(i/2). The second
component is taken from ith pixel. The third component is taken
from the first component of input pixel 2*floor(i/2)+1. In the
4224 case, the fourth component is taken from the third
component of each input pixel. This process is fully described
in the SGIX_subsample spec.
If the PixelStore parameter UNPACK_RESAMPLE_SGIX is set to
RESAMPLE_ZERO_FILL_SGIX then derived components are zeroed. Note that
subsampled components are co-sited with even numbered pixels,
and the odd numbered pixels produced have the zeroed components:
2424:
| | | | | | | |
| | o-----o | | | o-----o |
| | | | | | | |
| | | 0.0 | 0.0 | | | 0.0 | 0.0
| | | | | | | | | | | |
V V V V V V V V V V V V
< R0,G0,B1 > < R0,G1,B1 > < R2,G2,B3 > < R2,G3,B3 >
4242:
< A0,L0> < A3,L3 >
| | | | | | | |
\ / __\__/ \ / __\__/
X ___/ \ X ___/ \
/ \ / 0.0 \ 0.0 / \ / 0.0 \ 0.0
| | | | | | | | | | | |
V V V V V V V V V V V V
< R0,G0,B1 > < R0,G1,B1 > < R2,G2,B3 > < R2,G3,B3 >
Note that the parameter to DrawPixels should be even,
as should the value of UNPACK_SKIP_PIXELS, and
UNPACK_ROW_LENGTH. If any of these are odd then the error
INVALID_OPERATION is issued.
Additions to Chapter 4 of the 1.1 Specification (Per-Fragment
Operations and the Frame Buffer)
None.
Additions to Chapter 5 of the 1.1 Specification (Special Functions)
None.
Additions to Chapter 6 of the 1.1 Specification (State and State Requests)
XXX
Additions to the GLX Specification
Errors
XXX
New State
Get Value Get Command Type Initial Value Attribute
--------- ----------- ---- ------------- ---------
UNPACK_RESAMPLE_SGIX GetIntegerv Z4 RESAMPLE_REPLICATE_SGIX client
PACK_RESAMPLE_SGIX GetIntegerv Z4 RESAMPLE_REPLICATE_SGIX client
New Implementation Dependent State
None.
Revision History
Revision 1, July 27, 1999 - SGI internal revision #4.
Revision 2, January 27, 2015 - note that Khronos spec file values from
enums have been changed to match the extension spec (Khronos internal
bug 12653).